All elements in the universe are made of atoms. An atom is composed of a nucleus and electrons. A nucleus is composed of neutrons and protons. Some nuclei are stable, and some undergo spontaneous radioactive decay. Radioactive decay can also be induced by interaction with neutrons or other particles.

In nuclear reactors, heat is produced by fission of fissile nuclear materials like uranium-235. In this case, fission is induced when the nucleus absorbs a neutron, causing it to split apart. This produces fission products, including free neutrons, which can then split other uranium-235 nuclei. This chain reaction produces heat, via radiation, and the slowing down of fission products as they impact the fuel around them. Nuclear reactors are designed to convert this heat into electricity, like in any other thermal power plant. To avoid overheating, the plants incorporate cooling systems.

Nuclear fusion is another type of nuclear reaction in which extra energy is released when light nuclei are fused together. This type of reaction produces heat in the sun and other stars. Unlike the nuclear fission process, extreme temperatures and pressure are needed to initiate and sustain the fusion reaction, making it challenging, though research and development aimed at achieving controlled fusion has resulted in significant advances in recent decades.

Nuclear power is the largest source of low-carbon electricity in OECD countries, with an 18% overall share of electricity production in 2013. Globally, it is the second-largest such source, with an 11% share.

The generation of electricity using nuclear energy was first demonstrated in the 1950s, and the first commercial nuclear power plants entered operation in the early 1960s. Nuclear capacity grew rapidly in the 1970s and 1980s as countries sought to reduce dependence on fossil fuels, especially after the oil crises of the 1970s. However, with the exception of Japan and Korea, growth stagnated in the 1990s. Reasons for this included increased concerns about safety following accidents at the nuclear power plants at Three Mile Island (1979) and Chernobyl (1986), delays and higher-than-expected construction costs at some nuclear plants, and a return to lower fossil fuel prices.

However, from 2000, there was a renewed interest in nuclear power, and the pace of construction accelerated after 2005. At the end of 2010, there were 65 reactors under construction, and 60 new countries had expressed interest in launching a nuclear programme to the International Atomic Energy Agency (IAEA). Then, in March 2011, a major earthquake and tsunami ravaged the Pacific coast of northern Japan and damaged the cooling system at the Fukushima Daiichi nuclear power plant, resulting in a severe accident. No deaths have been attributed to the accident (while the tsunami and the earthquake killed 20,000 people), but serious releases of radioactive material resulted in contamination of the surrounding environment and led to the evacuation of several thousand inhabitants from their homes. In reaction, most nuclear countries announced safety reviews of their nuclear reactors (stress tests) and the revision/improvement of their plans to address similar emergency situations, including in the framework of the G8-OECD/NEA Ministerial Seminar on Nuclear Safety and Forum of Regulators of June 2011.

The impact on the growth of nuclear generating capacity will become fully clear only in the coming years. A limited number of countries (essentially Germany and Italy) have decided to eventually phase out nuclear power or to abandon their nuclear plant projects. But a majority of nations have confirmed their construction plans, including China, the Emirates, France, Poland, the United Kingdom and the United States, and the 72 reactors under construction at the start of 2013 were the most in 25 years.

What is the IEA view of nuclear power's future?

Nuclear power is a critical element in limiting greenhouse gas emissions. A mature, low-carbon technology, nuclear power is available today for wider deployment, subject to safety and security conditions. The present status of nuclear energy technology is the result of over 50 years of development and operational experience. Every country has a sovereign right to decide on the role of nuclear power in its energy mix. Nevertheless, nuclear is one of the world’s largest sources of low-carbon energy, and as such, has made and should continue to make an important contribution to energy security and sustainability. The scale of nuclear is such (an average nuclear plant has the production of 4000 windmills) that it is difficult to imagine nuclear being fully replaced by low-carbon renewables in the foreseeable future. Also, the intermittent nature of renewable energy production, particularly wind power and solar photovoltaic, together with planning and grid connection constraints, means its contribution will still need to be balanced by large-scale, low-carbon generation such as that made possible by new nuclear generation. Refer to the IEA-NEA Nuclear Energy Technology Roadmap for more information.

In addition, the World Energy Outlook warns that many countries must also make important decisions regarding the almost 200 nuclear reactors due to be retired by 2040, and how to manage the growing volumes of spent nuclear fuel in the absence of permanent disposal facilities. The expert technical and policy communities generally view deep geologic repositories as a viable solution to safely isolate the the longest-lived and the most highly radioactive waste from the commercial nuclear fuel cycle over the very long time periods required. National efforts to develop deep geologic repositories are at varying stages. To date, no country has fully implemented such a facility.

Are technologies under development for the next generation of nuclear systems?

Yes. Several technologies under development offer the potential for improved sustainability, economics, proliferation resistance, safety and reliability. Some will be suited to a wider range of locations and to potential new applications. Each involves a significant technological step, such as passive cooling, which cannot be disrupted, and will require full-scale demonstration before commercial deployment. Such systems could start to make a contribution to nuclear capacity from 2040.

Uranium supply is currently more than adequate to meet demand up to 2035 and beyond. However, given the long lead time of mining projects, the IEA-NEA Nuclear Energy Technology Roadmap recommends that investments and the promulgation of best practices continue to be made so as to develop environmentally safe mining operations. The current world market for fuel services (uranium supply, conversion, enrichment services, fuel fabrication) provides a considerable degree of security of supply and thus can play a major role in supporting the further development of nuclear energy.